1. Field of the Invention
This invention relates, generally, to control devices for prosthetic limbs. More particularly, it relates to a myoelectric control device having thousands of electrically conductive contacts for controlling a versatile prosthesis.
2. Description of the Prior Art
Early prosthetic devices intended to replace the human hand were mere hooks that had limited utility. Modern devices, however, are not much better. Typically, they include a pair of mechanical fingers and an opposable mechanical thumb that can perform a slow grasping action or a fast grasping action. The fingers and thumb are myoelectrically controlled, i.e., they receive electrical signals from electrodes placed on the patient's skin. These electrodes are sensitive to galvanic currents on the skin generated by muscles lying below the surface thereof. Thus, if an amputee quickly contracts his grasping muscles because he wants to grab something quickly, the electrodes can distinguish the electrical signals thereby generated from the signals that would be generated if a more casual contracting of the grasping muscles was made. In this manner, the amputee can select between the two rates of closing of the fingers and the opposable thumb.
Only three electrodes are employed in the above-described well known device, because the structure of the artificial hand and its abilities are so simple and limited. Each electrode is about three-eighths of an inch in diameter and is of metallic construction. Due to the size and metallic structure of the electrodes, it is not a simple task to maintain them in their proper position relative to the patient's skin. As the residual limb changes in size due to water retention or other factors throughout the day, or from day to day and month to month, the contact between the electrodes and the skin is affected; poor contact results in poor performance of the artificial hand.
There is a need, then, for an improved myoelectric control device. The improved device would have more than three electrodes so that better prosthetic hands could be developed. Moreover, the improved device would be mountable in such a way as to remain in full contact with an amputee's skin at all times the prosthetic device is worn.
However, at the time the present invention was made, it was not obvious to those of ordinary skill in this art how the needed improvements could be made, in view of the prior art when considered as a whole.